If the time that the ignition current flows through the ignition coil is determined solely by the pulse width of the pulses furnished by the above-described pulse generator, the pulse width may be too narrow to allow the current through the coil to reach the minimum value required for ignition or, if the pulse width is too wide, the current may flow for too long a time prior to ignition, thereby generating unnecessary heat losses, and decreasing the lifetime of a number of components.
Ignition systems are known, for example from German Disclosure Document DE-OS No. 2,448,675 or U.S. Pat. No. 3,587,551, in which some decrease of the undesired losses is achieved by limiting the current through the primary coil to the minimum value required for ignition until ignition takes place. This assures that the energy at ignition will always be the same, but does not decrease the losses described above.
It is an object of the present invention to provide an ignition control system wherein the closure of the series switch is controlled to assure the fact that the ignition current will have the necessary amplitude for ingition, but will not flow unnecessarily long prior to the ignition time. This object is to be accomplished regardless of variations in supply voltage, caused, for example, by changes in the charge of the battery, or changes in the parameters of the various components caused, for example, by temperature changes.